[sqlalchemy] Strange Error: FlushError: Instance Child at 0x1087b30 has a NULL identity key.
Hi everyone, I'm writing a script using sqlalchemy 0.66 and sqlite3.
In my script I'm trying to set up a one to one relation between two
tables via ORM. Here is a simplified code showing my situation:
from sqlalchemy import *
from sqlalchemy.orm import *
class Parent(object) :
def __init__(self, name) :
self.name = name
class Child(object) :
def __init__(self, name) :
self.name = name
engine = create_engine(sqlite:///test.db, echo=False)
metadata = MetaData(engine)
prn_tab = Table(parent, metadata,
Column('id', Integer, primary_key=True),
Column('name', String),
sqlite_autoincrement=True)
prn_tab.create()
chl_tab = Table(child, metadata,
Column('id', Integer, primary_key=True),
Column('name', String),
sqlite_autoincrement=True)
chl_tab.create()
fck = ForeignKeyConstraint
chl_tab.append_constraint(fck([chl_tab.c.id], [prn_tab.c.id]))
rel = relationship(Child, uselist=False, passive_deletes=True)
mapper(Parent, prn_tab, properties={child:rel})
mapper(Child, chl_tab)
Session = sessionmaker()
Session.configure(bind=engine)
session = Session()
session.add(Child(Carl))
session.commit()
if you run the above code you will see that the commit statement
generates the following error:
sqlalchemy.orm.exc.FlushError: Instance Child at 0x1087b30 has a
NULL identity key. Check if this flush is occuring at an
inappropriate time, such as during a load operation.
I really cannot understand the reason why this error is raisedcan
anyone give a hint? Tahnks in advance!
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Re: [sqlalchemy] Strange Error: FlushError: Instance Child at 0x1087b30 has a NULL identity key.
SQLAlchemy doesn't consider a primary key column that is also a foreign key to
another column to be autogenerating of a new primary key value. So it is
not fetched here due to the FK on child.id. If the SQLite database here had
foreign key constraints enabled the below operation would fail since there is
no parent id of 1 present.SQLite is unique in that such a pattern is even
allowed, not to mention you are tricking it by adding the FK constraint *after*
the create, so the error message isn't well tailored here, but since there is
already ticket 2170 to improve this, will add this contingency to the message.
On May 22, 2011, at 1:35 PM, Massi wrote:
from sqlalchemy import *
from sqlalchemy.orm import *
class Parent(object) :
def __init__(self, name) :
self.name = name
class Child(object) :
def __init__(self, name) :
self.name = name
engine = create_engine(sqlite:///test.db, echo=False)
metadata = MetaData(engine)
prn_tab = Table(parent, metadata,
Column('id', Integer, primary_key=True),
Column('name', String),
sqlite_autoincrement=True)
prn_tab.create()
chl_tab = Table(child, metadata,
Column('id', Integer, primary_key=True),
Column('name', String),
sqlite_autoincrement=True)
chl_tab.create()
fck = ForeignKeyConstraint
chl_tab.append_constraint(fck([chl_tab.c.id], [prn_tab.c.id]))
rel = relationship(Child, uselist=False, passive_deletes=True)
mapper(Parent, prn_tab, properties={child:rel})
mapper(Child, chl_tab)
Session = sessionmaker()
Session.configure(bind=engine)
session = Session()
session.add(Child(Carl))
session.commit()
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